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071011-001 - Vise Glue splicing and viscosity tests
Date 11th October 2007
Tested by GK.
Location Sydney, Australia
Test Procedure Burst Test
References http://www.aircommandrockets.com/day46.htm
Related N/A

Aim

  • To see if VISE glue is suitable for splicing.
  • To test how VISE's viscosity can be altered to make it suitable for splicing.
  • To measure the burst pressure of a splice made with VISE glue.

Experiment Setup

  1. A normal bottle splice is made with the VISE glue, and then hydrostatically tested for burst pressure.
  2. A set of VISE glue and additive mixes are placed on an inclined plane to see how viscous they are over time. A control is used to compare against normal VISE.
  3. The optimal VISE glue mix is then used to make a regular splice and hydrostatically tested to burst pressure.

Test #1 - VISE only splice

We spliced a pair of 1.25L bottles using the symmetrical splice technique using the VISE glue only. The glue has the consistency of honey (also as messy) and remains quite runny for at least a couple of hours. When  the splice was first made it all looked good for the first 10 minutes, but then the glue started dripping from the joints and continued to do so. This glue slightly expands as it cures and this expansion kept forcing the glue out of the joints.

In an attempt to stop the glue from leaking, water was poured on the inside and outside to cure it quicker. VISE like PL cure with atmospheric moisture. This bubbled up the glue within minutes but did not solidify it. In the end it became a large mess with a lot of glue leaking out of the joints.

We let the splice cure for a week and then did a hydrostatic test to see if it could hold any pressure. The splice began to leak at 20 psi from a number of "channels" that developed while it was curing. Because the leaks were only minor we pressed ahead with the test and reached 100psi. At this point the water was leaking too fast from the bottle that more pressure could not be applied and so the test was aborted. Although the splice leaked it held well.

VISE polyurethane glue.
VISE glue was used to splice two bottles. Straight VISE is too messy.
After 2 hours the glue finally set but not before spilling everywhere..

This splice held at least 100psi but had a number of small leaks.

Test #2 - Changing the viscosity of the VISE glue

After a number of discussions with Damo, Trevor, Clifford, Richard and David about how to increase the viscosity using a very fine powder we finally chose a material we had on hand called Polyfilla. The main website is here.

Please refer to the time-lapse diagram below:

We mixed the glue with the powder in a 1:1 ratio by volume until it was thoroughly mixed. We then took half of this mixture and added a couple of drops of water and thoroughly mixed that in.

We then also thoroughly mixed the glue and powder in a 1:2 ratio by volume.

Along with a blob of PL Premium and the VISE glue by itself we placed these mixtures on a 25 degree incline, and took photos periodically to see how it flowed.

Pollyfilla powder was used in different proportions to see if the VISE glue could be made thicker.
Over a period of two hours different proportions of glue and powder were tested for viscosity. PL Premium was used as a control.

The results

  • PL Premium did not flow at all over a 2 hour period. After two hours it was still soft although had slightly skinned over.
  • The VISE glue kept flowing slowly and at close to the 2 hour mark bubbles started appearing in the drop. After 2 hours the glue was still sticky to the touch.
  • The 1:1 mix with water added solidified the fastest but it had also bubbled up the most. After two hours it was quite hard, but resembling a meringue. It did not flow at all.
  • The 1:1 mix without water was still quite runny after 2 hours but not as much as the VISE glue by itself. The bubbling was also quite minimal. It was still slightly sticky after 2 hours.
  • The 1:2 mix did not flow but had the consistency of dough. It also looked like it didn't have very high adhesion properties. After 2 hours it was not sticky but was still soft.

All the samples were left overnight and by the next day they had all solidified.

Test #3 - Splicing with a 2:3 mix, and pressure test

Test #2 showed us that it was possible to considerably thicken up the VISE glue but the 1:1 ratio was too runny and the 1:2 was too dry so we chose a 2:3 ratio as the mix we would go with for a test splice.

We mixed up about 15ml by volume of polyfilla and 10ml of glue. This turned out to be about the right amount for 1 splice. The mixture was very thoroughly mixed into an almost paste consistency.

Splice made with 2:3 mix ratio of VISE glue to Polyfilla powder. The gaps seen here were filled in as the glue expanded.
A contrast enhanced view of the cured glue mix in the splice.
A contrast enhanced view of cured PL Premium in a splice. Note the difference in bubble size.
Ready to hydro-statically test the 2:3 mix splice. Cure time was 5 days.
After reaching 170 psi the splice still held. Burst test was aborted due to too much air in the bottles. These bottles typically burst at 190 psi.
You can see how much the bottles stretched at the neck while still retaining a good bond in the splice.

The splice

Two 1.25L bottles were spliced again using the symmetrical splice technique. The splice sleeve was made from a heat shrunk 1.5L bottle. The width of the splice was around 120mm. All surfaces were lightly sanded.

The glue paste was easy to apply to all the surfaces with just a skewer stick. All the surfaces were completely coated with the paste before being brought together. Excess glue was wiped off. We also put a ring of sticky tape on the inside edge of the curl of one of the bottles. This was going to help contain any glue dripping from the inside joint.

At first there were a number of gaps that didn't have much glue in the splice, but as the glue cured it expanded and filled these gaps.

The final cured glue pattern can be seen above. Compare that with an identical splice done with PL Premium. There appear to be much larger air pockets, compared to PL's smaller bubbles.

We let the splice cure for 5 days before testing. As you can see from the photos there were no drips and only a little expansion around the edges that can be easily removed.

Burst Test

After 5 days we set it up on the hydrostatic test stand and pressurised it. We went up to 100 psi and  held there for 1 full minute. There were no leaks and the pressure remained steady.

We then slowly increased the pressure all the way up to 170 psi! (11.7 bar ) The splice was still holding although from what I could see from the distance there might have been an almost insignificant leak in the splice as a few drops started to appear on the side. At this point air started entering the bottles as they were quite stretched and so the test was aborted.

The photos above show how much the bottles stretched around the neck when compared to a similar bottle.

Conclusions

  • The biggest problem with the VISE glue is its low viscosity, as it can create quite a mess of drips as it cures slowly.
  • These tests showed us that the VISE glue is a very effective glue for gluing PET and at least here in Australia it is a viable alternative to PL Premium when it is mixed with a powder to make it easy to work with.
  • We would be quite comfortable flying these splices at 140 psi. The open question still is what shock resistance the splice has for rockets returning to Earth.
 

 



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